As a vacuum valve that has the primary side used under vacuum conditions and the secondary side used under atmospheric pressure conditions and is opened when the fluid pressure on the primary side exceeds a set value, PTL 1 discloses a vacuum valve including a body provided with a primary side passage and a secondary side passage, a cylindrical casing provided on the body, a valve element opening or closing communication between the primary side passage and the secondary side passage by moving upward or downward, a stem moving upward or downward integrally with the valve element, opening pressure setting means setting a set value of a fluid pressure in the primary side passage beyond which the communication is opened, and forcible opening means forcibly opening the communication regardless of the fluid pressure in the primary side passage, in which the forcible opening means is a manual handle.
In such a vacuum valve, the forcible opening means is desirably automatic (using compressed air). To achieve such a vacuum valve of automatic forcible opening type, combination with, for example, the vacuum valve of manual forcible opening type described in PTL 1 and the vacuum valve using compressed air described in PTL 2 is considered. The vacuum valve described in PTL 2 does not have opening pressure setting means that sets a set value of the fluid pressure in the primary side passage beyond which communication is opened.